1. Field of the Invention
The present invention relates to an apparatus for predicting the lifetime of cables arranged in movable portions such as arm portions of an industrial robot.
2. Description of the Related art
Cables for movable portions are arranged in the arm portions of an industrial robot so that the arm portions can be moved. Since each of the cables for the movable portions of the type described above is given bending stress and torsional stress when the arm portions move, the cables for the movable portions suffer from a problem in terms of their short lifetime.
If an industrial robot in which a strand constituting the cable has been broken due to the expiration of the lifetime were continued to be used, the operation of the industrial robot is stopped, causing the production line using the same to be also stopped. Alternatively, an error taking place during the operation of the robot can damages the outer equipment, causing an accident resulting in injury or death in the worst case.
Hitherto, a variety of apparatuses capable of detection of the breaking of the cable have been disclosed. For example, there has been an apparatus disclosed in Japanese Patent Laid-Open No. 62-165158, the apparatus being capable of detecting the breaking of an output cable of a rotary encoder which is provided for the purpose of detecting the angle or the position of the arm or the like of an industrial robot. Another apparatus capable of detecting the breaking of the cable arranged in a resistance welding machine has been disclosed in Japanese Patent Laid-Open No. 62-245162.
However, since the above-disclosed conventional apparatuses for detecting the breaking of a cable are arranged simply to detect the breaking of the cable, they cannot predict the breaking of the cable depending upon the result of the detection of the lifetime of a cable, that is, the state of the fatigue of the cable.